Method and apparatus for melting batch materials

Abstract

 The invention discloses a method of creating a new different temperature profile in a pot furnace for production of glass metal for manual processing as well as a pot furnace in accordance with the new method. The method and the pot furnace eliminates several causes of glass defects. The pot furnace is designed to maintain the desired new temperature profile during the melting process and can utilize electricity, gas or oil for heating.

Description

[0001] The present invention relates to a method for melting batch materials at the glassworks. More particularly the invention relates to a method of creating a new different temperature profile in a pot furnace for glass metal production, which eliminates several glass defect causes, as well as to a pot furnace in accordance with this new method.

PRIOR ART

[0002] Glass metal for manual processing by glass-blowing is produced in a furnace by melting batch materials in a pot or a tank at a temperature of about 1400°C. Besides a refining agent, which produces gas for creating a certain amount of turbulence in the melt, the batch contains the basic ingredients for the glass metal. This turbulence is intended for creating a stirring effect in the melt which then improves the possibility to achieve a high quality glass metal containing no defects. Furnaces for this purpose are disclosed in a number of published patents, for example in CH-173 332, GB-1 121 778, US-941 148, US-2 761 890, US-3 742 111, US-4 143 232 and DE-1 796 039, respectively.

[0003] All of these patents except for the disclosed Swiss patent CH-173 332 presume use of a tank, while the present invention is intended for a pot. With the exception of the patent US-941 148 disclosing a tank for a gas or oil heated furnace the other five disclosures referred to, do have a tank with electric electrodes within the melted glass metal. Such melting procedures from a view of industrial welfare are not directly suitable for manual processing of the glass metal as the glass-blower is subjected to the risk of an electric shock when gathering glass metal out of the melt since the pipe, which is used, is made of conductive metal.

[0004] The Swiss disclosure CH-173 332 is related to strong heating of the upper part of the batch which has proven to be an incorrect method as the refining agent at the top of the batch disappears directly into the air and will therefore to a large extent be consumed before the batch is melted into a glass metal. This disclosure further indicates that electric heaters will be placed simply above and below a pot, respectively. Besides, according to what was pointed out previously, viz. that the heater above the pot will have an unfavorable effect on the melting, this arrangement also results in glass vapour very easily forming a layer of glass covering the heater dripping back into the pot if this is of the open type and thereby introducing cords. Heating from below is better but the arrangement according to this invention may be dangerous as the method suffers from the constraint that the position of the electric heater easily permits glass metal in the pot to obtain an electric potential through creeping currents. Additionally, it is inevitable that hearth glass spill will enter into the space underneath the pot resulting in a short-circuiting of the heaters after some time due to the accumulation of hearth glass spill.

[0005] Prior art gas or oil heated furnaces were often used for the reason that it was asserted that the temperature in an electric furnace is too uniform to be able to produce real high quality glass. This is incorrect as primarily the quality of the glass produced will highly depend on the creation of the proper temperature profile in the furnace and consequently in the pot.

[0006] Another constraint of the furnaces according to the prior art is that only a part of the melted batch can be used, resulting in a need for certain furnaces to have up to 30% residue in the pot for each new cycling, and additionally these furnaces necessitate mixing of the batch with cullets to obtain a glass metal of an acceptable quality.

[0007] The trick for producing high quality glass metal is to create a proper temperature profile in the furnace to ensure a correct melting procedure for the batch and thereby to utilize the refining agent optimally. The proper temperature profile will then minimize the stirring or rotation of the fully melted glass metal in the pot to a low desired amount which will as a result reduce or avoid creation of cords and seeds, and consequently result in a production of very high quality glass and at the same time achieving a very high efficiency in the process of utilizing the gases produced by the batch.

SUMMARY OF THE INVENTION

[0008] The present invention is disclosing a method to melt the batch in the process of glass metal production for manual glass processing, which in a pot furnace creates a temperature profile forming a melting process resulting in a melted glass metal, which contains very high quality glass metal from the top to the bottom of the pot.

[0009] According to the present invention there is also provided a pot furnace, using electric or gas/oil heating, which is adopting the new temperature profile to obtain very high quality glass metal all the way to the bottom of the pot and which does not require mixing of the batch with cullets and in which the residue will amount to 2 % or less.

[0010] Additionally, in a pot furnace according to the present invention the temperature is redistributed within the furnace and accordingly around the pot in such a way that the melting of the batch proceeds in the pot essentially from below and from the sides, whereby the refining agent will be optimally utilized especially in the lower part of the melt, and the gas forming seeds will early escape from this part as the melting process essentially proceeds from the bottom and the lower parts of the side walls of the pot and upwards.

[0011] By melting the batch in such a way, the gas achieved from the refining agent can more easily escape since it only has to move through a limited part of the melt and will then efficiently be vented through the still unmelted batch contrary to the commonly used procedure where the batch essentially melts from above and the produced gas in the form of seeds will have a progressively longer path for escaping from the melted glass metal resulting in the fact that a considerable part of such a melt will not produce an acceptable glass quality.

[0012] In an electric pot furnace, the new temperature profile is achieved partly by a matching design of the furnace chamber and with electric heaters arranged vertically aligned, i. e. in a circle around the pot without touching the pot or the sidewalls or bottom wall of the furnace chamber. The pot is for example placed on top of a number of supports having such a height over the bottom wall that direct radiation from the vertically aligned electric heaters extend below the bottom surface of the pot, and the radiation from those will principally access most of the bottom surface of the pot. The other part of this design uses cooling air for the terminal inlets of the electrical heaters and is adapted to be blown along the heaters, thereby reducing radiation and blowing convection air (heat) downwards in the furnace and depending on the somewhat stronger cooling of the upper portions of the heaters, additionally slightly lowering the electric resistance in that portion, will result in a slightly lower power and consequently lower temperature in the upper part of the furnace chamber. Correspondingly the lower portions of the electric heaters will have a slightly higher electric resistance and a corresponding higher temperature at a constant voltage over the electric heaters. The electric heaters are electrically controlled in a conventional fashion.

[0013] In a gas or oil heated pot furnace the new temperature profile is achieved partly by a matching design of the furnace chamber along with the main design for the electric furnace and partly by arranging a first lower burner at one end of a first heating channel discharging into a space under the pot, and at least one secondary upper burner in at least one secondary channel discharging into the upper and middle portions of the furnace chamber maintaining the temperature profile in the chamber at a properly balanced furnace pressure to permit easy gathering of glass metal through the gathering opening with low heat outlet. The first heating channel is sloping slightly downwards to prevent hearth glass spill from reaching the burner in case of large amounts of hearth glass spill entering the furnace chamber. If hearth glass spill should reach the burner there is a great risk that it would be damaged and the operation of the furnace would be jeopardized. The burners are controlled, i. e. electrically, in a conventional fashion.

[0014] The supports on which the pot is placed are arranged in such a manner that the pot will lean about 5 cm towards the furnace door containing the gathering opening. Firstly, this implies that radiation/convection heat towards the front side of the pot will be increased, and secondly that the pot will be prevented from migrating backwards into the furnace chamber which otherwise sometimes is the case for pots with a mouth. At the same time, providing a larger distance between the pot and the door results in a higher temperature at the front side of the pot, the pot must still be readily accessible for a glass-blower's pipe to facilitate gathering of glass metal also deep down into the pot.

[0015] In order to more easily create such a well defined distance the pot is provided with a mouth or an elevated inclined edge projecting towards the gathering opening. This mouth of the pot prevents the batch and gathered glass from escaping between the pot and the inner side of the door and thereby after some time destroying it. Besides, at the same time it prevents glass from flowing back to the melt and introducing cords in the melt. Furthermore, the lower edge of the gathering opening is lowered to a level below the lower surface of the mouth of the pot whereby a matched stone, for instance suitable brick, is placed for a properly matched interference between the mouth of the pot and the lower portion of the gathering opening. As the different pots shrink by different amounts there will always be chosen a suitable measure of the stone and a fibre mold to achieve adequate sealing between the pot and the gathering opening resulting in minimizing the largest source of heat loss in such a pot furnace.

[0016] To compensate for the heat loss at the front of the furnace and to maintain the preferred temperature profile, the distance between the vertically aligned electric heaters is decreased at the front side of the furnace chamber. Similarly, in the gas and oil heated furnace the secondary burner/burners is/are positioned to deliver more energy at the front side of the furnace chamber.

[0017] This method and the pot furnace according to the method provide in addition to a more energy saving heating system of a pot furnace for glass metal also the following benefits:

a. the batch will be used without mixing with cullets;

b. the batch will be refilled for a new cycling without the necessity of having a residue of glass in the pot;

c. exclusively the batch will be put in the pot;

d. seeds and stones do not have to be removed from the larger pieces of glass for eliminating glass defects in a final product;

e. the quality of the produced glass metal is such that no part of this will have to be discarded nor will finished glass products have to be discarded due to glass defects.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention will be described by preferred embodiments to be contemplated with reference to the accompanying drawings wherein like reference numerals are used throughout to designate like parts. In the drawings:

Fig. 1 illustrates a vertical cross section of an embodiment of an electrically heated pot furnace with an open or a semi-open pot according to the present invention;

Fig. 2 illustrates a horizontal cross section of a pot furnace along the line II - II in Fig. 1;

Fig. 3 illustrates a vertical cross section of an embodiment of a gas or oil heated pot furnace according to the present invention;

Fig. 4 illustrates a vertical cross section along the line I - I in Fig. 3;

Fig. 5 illustrates a horizontal cross section of the furnace in Fig. 4 showing a first embodiment of a heating chamber under the pot;

Fig. 6 illustrates a horizontal cross section of the furnace in Fig. 4 showing a second embodiment of a heating chamber under the pot;

Fig. 7 illustrates a horizontal cross section of the furnace in Fig. 4 showing a third embodiment of a heating chamber under the pot;

Fig. 8 illustrates a vertical cross section of a gas or oil heated pot furnace according to a fourth embodiment of a heating chamber under the pot; and

Fig. 9 illustrates a horizontal cross section of the furnace shown in Fig. 8.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0019] A pot furnace according to the present invention comprises a furnace body 10 with a furnace door 11 incorporating a gathering opening 12. The furnace body defines a chamber by an inner wall 20, an upper floor surface 21 and a ceiling 22. The chamber is heated by a number of electric heaters 30 or gas or oil burners 32, 33 to a temperature in the order of 1400°C. Inside the chamber is placed a pot 40 which is filled with batch materials to be melted into a glass metal. The pot 40 can be either of a semi-open or an open type.

[0020] The upper floor surface 21 in the pot furnace contains in a first embodiment four supports 25 onto which the bottom surface 41 of the pot 40 is resting. These supports 25 are designed in a manner that the upper end surfaces of the supports forming a slightly inclined plane towards the furnace opening 12. The pot is thereby given a slight inclination forward of about 5 cm measured horizontally between the vertical planes of the bottom and top edge.

[0021] In a first embodiment electric heaters 30 are arranged hanging vertically down from the ceiling 22 of the furnace chamber along a circle of a diameter substantially larger than the outer diameter of the pot 40 and thus encircling the pot 40, as shown in Fig. 2, which is a cross section along the line II - II of Fig. 1. In this embodiment there are 12 equidistant heaters, but in a further preferred embodiment the number of heaters 30 may be different and distributed at different distances to each other to compensate a larger heat loss close to the furnace door 11 containing the gathering opening 12.

[0022] The heaters 30, i.e. the KANTHAL SUPER manufactured by Kanthal AB at Hallstahammar, Sweden, are vertically arranged such that their lower portions 31 are positioned at a predetermined distance above the upper floor surface 21 and in the same manner there is a predetermined distance between the heaters 30 and the side walls 20 of the furnace chamber. Additionally, the heaters 30 are arranged such that the lower portions 31 are positioned well below the bottom surface 41 of the pot 40 such that the bottom surface 41, except for the contact surfaces on top of the supports, will be fully exposed to direct heat radiation from the heaters 30.

[0023] Each heater 30 has a power inlet 34 or an electric terminal at a roof surface 23 with an arrangement to force air into the inlets 34 preventing glass from condensating between the terminals at the inlets 34 causing electric arcing, which destroys the power terminals as well as the hole in the brick-built roof of the furnace carrying the heaters. In the preferred embodiment this air is utilized blowing along the heaters such that each upper portion 30a of the heater will be cooled, whereby the heater due to a different temperature of the upper and lower portions will also be presenting slightly different electric resistances in these portions, and at a constant voltage across the heaters 30 those will produce a slightly higher power in the lower portions 30b compared to the upper portions 30a, which then are showing different electric resistances. In this way a temperature gradient is achieved along the heaters 30 and consequently a changed temperature profile is created inside the furnace chamber containing the pot 40.

[0024] This together with the arrangement having the bottom surface 41 of the pot directly exposed to radiation heat from the lower portions 30b of the heaters will further emphasize the desired temperature profile in the furnace, such that the furnace chamber will in an initial state have at least equal or higher temperature around the lower parts of the pot 40 compared to the rest of the chamber. According to this method it is ensured that the batch in the pot 40 is melted essentially from below and from the sides of the pot, whereby the refining agent will be optimally utilized especially in the lower part of the melt, and the gas forming seeds will early escape from this part as the melting process essentially proceeds from the bottom part of the pot and the lower part of the side walls and upwards.

[0025] By putting the heaters 30 into electric arrays, i. e. such that each third heater is fed from a common phase in a standard 3-phase system, a turbulence can be created in the furnace chamber by controlling the power of each array and thereby achieve that the turbulence in the glass metal will get a proper appearence.

[0026] In a second embodiment of the pot furnace using gas or oil heaters, shown in Fig. 3, there is formed a chamber 35 underneath the pot 40. In the floor surface 21 there is then formed an opening 26 having a diameter less than the outer diameter of the pot 40. Consequently the pot will primarily be carried by an edge surface around its bottom surface 41.

[0027] In the furnace there is arranged a first channel 36, which discharges into a chamber 35 underneath the pot for heating of the pot 40. This channel is arranged inclined downwards and directed towards the chamber 35 and is, at the other end, provided with a first gas or oil burner, positioned at a level corresponding to the level of the floor surface 21 (or higher up) to prevent glass metal from flooding the burner if the pot should crack. In the upper portion of the furnace, there is additionally formed at least one secondary channel 37 supplying heat from at least one secondary burner 33 to the rest of the furnace chamber.

[0028] In the pot furnace according to Fig. 5, the channel 36 seen from above is tangentially feeding the chamber 35, while in a third embodiment this channel for heating is radially feeding the chamber 35. In Fig. 6, a third embodiment is demonstrated in which the channel 36 forms part of a loop underneath the pot 40, which then will experience an additional support under the bottom surface 41, further decreasing the strain on the bottom surface of the pot, but with some loss of efficiency in the general heating of the bottom surface. In Fig. 7, a corresponding arrangement is demonstrated but in this case the middle of the bottom surface is supported by a couple of supports 61 to obtain more space for the hot gases from the burner 32 to reach most of the bottom surface 41 of the pot 40.

[0029] In Figs. 8 and 9, a fourth embodiment is demonstrated having the pot resting on a number of supports 62 similar to the supports 25 of the first embodiment in Fig 1. Channels 36 and 37 respectively with gas or oil burners 32 and 33, respectively, deliver heat to the furnace chamber in a predetermined manner to maintain the preferred temperature profile in the furnace chamber with an initially higher temperature in the lower portions of the furnace.

[0030] The pot is in the preferred embodiment provided with an elevated edge or a mouth 45. The lower inner surface of this edge or mouth 45 is inclined outwards and downwards. The furnace door 11 containing the gathering opening 12 is arranged such that an edge surface 13 of the gathering opening 12 is levelled below the lower edge surface of the mouth 45, and a suitable stone or brick is fitted on the edge surface 13 together with a fibre mold to achieve a sealing between the upper front of the pot and the gathering opening 12.

[0031] The pot furnace according to a preferred embodiment is additionally provided with a vertically arranged channel 50 exiting into a pocket for hearth glass. This exit channel consists of a first portion 51 starting out in the chamber 35 underneath the pot and a second portion 52 having a larger cross section discharging into the pocket for hearth glass spill while the hot exhaust emissions from the furnace are carried out separately through one or several exhaust channels, to for example a chimney.

[0032] Because of the inclination of the upper surface of the mouth and the fact that the pot itself is slightly inclined forwardly in the preferred embodiment due to the shape of the supports 25, 61, 62, gathered glass spill is prevented from flowing back into the pot introducing cords. Additionally the stone prevents batch and glass spill from escaping between the pot 40 and the furnace door 11. Besides preventing glass metal from accessing the inner side of the furnace door, the possibility to maintain the proper temperature around the pot is improved especially since the region around the gathering opening 12 is the area of the essential heat loss.

[0033] In an electric test furnace using an open pot having a diameter of 900 mm and a height of 700 mm there was achieved a percentage of defects in the glass metal of less than 2% when about 600 kg of glass metal was processed per day, and this from the top to the bottom of the pot. The power consumption during 24 hours of operation was 1 400 kWh, resulting in about 2.3 kWh per kilogram of glass with a density of 2.9 kg/dm³. The produced type was 24% lead crystal glass.

[0034] The above described preferred embodiment can, by those familiar with the technique, be varied and modified in many ways within the true spirit of the present invention and within the scope of the appended claims.

Claims

1. A method for melting of batch materials in a pot (40) inside a furnace (1) for production of glass metal to be used for manual processing, comprising
   filling of the pot (40) with the batch to be melted into glass metal;
   heating of the pot to achieve melted glass metal, characterized in
   forming of a temperature profile in the pot such that the melting of the batch in the pot (40) is primarily effected from the bottom and upwards and simultaneously from the side walls and inwards inside the pot (40), said temperature profile achieved by arranging a space region between the pot (40) and an upper floor surface (21) in the furnace and thereby initially heating this region to a slightly higher temperature than the rest of the furnace chamber, whereby the melting of the batch is proceeding essentially from below and from the sides of the pot towards the upper portion of the pot.

2. The method according to claim 1, wherein the pot furnace comprises a variety of vertically hanging electric heaters (30) each of which is equipped with its own power inlet (34) arranged around the pot (40), characterized in that the bottom of the pot is exposed to heat directly radiated from the heaters (30).

3. The method according to claim 2, characterized in that cooling air primarily utilized to prevent the condensation of glass at the power terminal inlets (34) of the heaters is blown along the heaters (30) for cooling of said heaters downwardly such that the electric resistance of the heaters is varied and gradually is increased towards a lower portion (30b, 31) of the heaters, whereby the emitted power at constant voltage across the heaters will correspondingly increase downwards the heaters.

4. The method according to any of claims 1 - 3, characte-rized in that the heaters (30), which are present in the furnace (1) encircling the pot are arranged at different distances from each other, the distances being dependent on the position of the heaters in relation to a gathering opening (12) positioned at a furnace door (11) in the pot furnace (1) and being closer to each other where the heat loss is largest.

5. The method according to claim 1, wherein the pot furnace comprises a variety of gas or oil burners (32, 33) arranged at the furnace (1), characterized in that a first burner (32) is heating the bottom of the pot (40) while a secondary burner/secondary burners (33) is/are maintaining the proper initial temperature profile in the upper portion of the furnace chamber.

6. A pot furnace utilizing the method in any of claims 1 - 5, comprising:
   a furnace body (10) with a furnace chamber, a furnace door (11) and a gathering opening (12), the furnace chamber comprising an inner wall (20), an upper floor surface (21) and a ceiling (22)
   a pot (40) for receiving the batch to be melted and comprising side walls and a bottom surface (41), characterized in that heaters (31, 32) are positioned such that the bottom surface (41) of the pot is fully exposed to heating from at least one heater simultaneously as the pot (40) is exposed to the rest of the heaters to maintain the initial proper temperature profile acting to melt the batch essentially from below and from the sides of the pot towards the upper portion of the pot, whereby the refining agent is optimally used in the lower part as well as in the upper part of the melted glass metal and the gas forming seeds will early escape from the lower part as the melting process essentially proceeds from the bottom and lower part of the side walls of the pot and upwards.

7. The pot furnace according to claim 6, comprising electric heaters arranged hanging vertically aligned from the ceiling (22) of the furnace chamber, characterized in that the pot (40) is arranged above the upper floor surface (21) on top of supports (25) and that the electric heaters encircling the pot are exposing lower portions (31) extending towards the upper floor surface (21) beyond the bottom surface (41) of the pot, ensuring that the bottom surface (41) will be fully exposed to direct radiation from the lower portions of the heaters (30).

8. The pot furnace according to claim 7, characterized in that the distance between the electric heaters (30) present in the furnace (1) and encircling the pot are arranged at different distances from each other, the distances depending on the position of the heaters in relation to the gathering opening (12) positioned at a furnace door (11) in the pot furnace (1) and being closer to each other where the heat loss is largest.

9. The pot furnace according to any of claims 6 - 8, characterized in that the electric heaters (30) are arranged into arrays each connected to its separate power feeding line to facilitate differentiated feeding of power to each one of such arrays.

10. The pot furnace according to claim 6, comprising heaters supplied with gas or oil, characterized in that below the lower surface (41) of the pot there is arranged a chamber (35) which is supplied with heat through an inclined channel (36), whereby a first burner (32) is arranged at one end of the channel, and the other end of the channel is discharging into the chamber (35) underneath the pot (40), and at least one secondary channel (37) is supplying the furnace chamber with heat by having a secondary burner (33) at a first end, and the other end discharging into the furnace chamber.

11. The pot furnace according to claim 10, characterized in that the chamber (35) is formed by an intercommunication opening in the floor and having a diameter less than the outer diameter of the pot (40).

12. The pot furnace according to claim 10, characterized in that the chamber (35) comprises support members (61, 62) supporting the pot (40).

13. The pot furnace according to any of claims 10 - 12, characterized in that the channels (36, 37) are discharging radially or tangentially into the furnace or discharging into the furnace utilizing a combination thereof.

14. The pot furnace according to any of the preceding claims 6 - 13, characterized in that the gathering opening (12) is formed in such a way that a matching stone (60) can be fitted to the side wall of the pot to prevent the batch or gathered glass from entering into the furnace chamber between the pot (40) and the furnace door (11) in addition to preventing undesired heat loss.

15. The pot furnace according to any of the preceding claims 6 -14, characterized in that the pot is provided with a mouth (45) or an elevated edge to accomplish a distance between the pot (40) and the furnace door (11).

16. The pot furnace according to any of the preceding claim 6 - 15, characterized in that the lower inside surface of the mouth (45) of the pot or the elevated edge is outwardly inclined downwards to prevent glass metal from flowing back into the pot (40).

17. The pot furnace according to any of the preceding claim 6 - 16, characterized in that the pot (40) is arranged slightly inclined towards the furnace door to further increase the space between the pot and the furnace door in order to better maintain the proper temperature profile.

18. The pot furnace according to any of the preceding claims 6 - 17, characterized in that an exit channel (50) leading into a pocket for hearth glass spill is arranged vertically and presents a first part (51) beginning in the chamber (35) underneath the pot and a second part (52) of a larger cross section discharging into the pocket for hearth glass spill.

Drawing